The 88-year-old made the announcement in an open letter dedicated to "friends and fellow Americans," writing, "As this condition has progressed, I am no longer able to participate in public life. Since many people have asked about my current status and activities, I want to be open about these changes, and while I am still able, share some personal thoughts."

O'Connor, who served on the Supreme Court from 1981 to 2006, went on to describe her commitment to advancing "civic learning and engagement" that continued in the 12 years since her retirement. As she writes, it's that commitment that led her to launch the organization iCivics, which teaches the core principles of civics to middle and high school students.

"I can no longer help lead this cause, due to my physical condition. It is time for new leaders to make civic learning and civic engagement a reality for all," she wrote, also calling for citizens, state, and federal governments to work together to fund the cause. "It is my great hope that our nation will commit to educating our youth about civics, and to helping young people understand their crucial role as informed, active citizens in our nation."

In the letter, the former Supreme Court justice — who says she will continue to live with friends and family in Phoenix — also expressed deep gratitude and appreciation for her governmental experience.

"How fortunate I feel to be an American and to have been presented with the remarkable opportunities available to the citizens of our country," she wrote. "As a young cowgirl from the Arizona desert, I never could have imagined that one day I would become the first woman justice on the U.S. Supreme Court."

During her tenure on the Supreme Court, O'Connor served as the decisive vote in a variety of important cases. She ruled on matters such as the upholding of Roe v. Wade, the Florida recount in the Bush vs. Gore election, and the use of affirmative action in university admissions, among many others. In 2009, then-President Barack Obama awarded O'Connor with the Presidential Medal of Freedom, the highest civilian honor in the country.

On Tuesday, Chief Justice John Roberts released a statement in response to news of her diagnosis. "Justice O'Connor is of course a towering figure in the history of the United States and indeed the world," he said, per The Washington Post. "She broke down barriers for women in the legal profession to the betterment of that profession and the country as a whole."

He also went on to add, "Although she has announced that she is withdrawing from public life, no illness or condition can take away the inspiration she provides for those who will follow the many paths she has blazed."